X-ray testing and measuring method and apparatus



X-RAY TESTING AND MEASURING METHOD AND APPARATUS Filed March 14, 1950QM, @uw

ATTORNEYS Patented Sept. 7, 1954 X-RAY TESTING AND MEASURING METHOD ANDAPPARATUS Frederic Fna, New York, N. Y., assigner to X-Ray ElectronicCorporation, New York, N. Y., a corporation oi New York Originalapplication November l, 1944, Serial No.

Divided and this application March 14, 1950, Serial N0. 149,515

5 Claims. (Cl. Z50-71) This application is a division of my copendingapplication Serial No. 561,361, filed November l, 1944.

This invention relates to X-ray devices and more especially to suchsystems using electron tube amplifiers controlled by an X-ray beam.

A principal object of the invention is to provide a specially designedtesting system using X-rays, wherein the response to the X-rayexcitation can be amplified with great stability and sensitivity.

Heretofore, intesting and measuring systems using X-rays as anexcitation source, variations in the power supply for the X-ray tubehave usually been considered a source of trouble. For example, where theanode or target voltage of the X-ray tube is derived from a rectifiedand nltered A. C. power supply line, any imperfect filtering has beenconsidered a drawback to be sedulously avoided. It has likewise beenconsidered a drawback that the X-ray tube be energized by raw A. C.Where the output of the X-ray tube exhibits an A. C. component, thereresults a variable width of the resultant X-ray spectrum and acorresponding variation in the X-ray intensity.

It is a principal object of this invention to utilize the alternatingcurrent component of the X-ray excitation as a useful adjunct to enablethe excitation response to be translated and amplified by stable andhighly selective alternating current amplifiers.

Another object is to provide a method of translating and amplifying theX-ray excitation response for the purpose of increasing the sensitivityof the testing or measuring system as a whole.

A feature of the invention relates to an improved system for testinguniformity or the lack of uniformity of articles through theintermediary of an X-ray source and an electric wave amplifier.

Another feature relates to a. method of using an X-ray tube as a testingsource in conjunction with a. stable alternating current electron tubeamplifier.

A still further feature relates to the novel organization, arrangementand relative location of parts which cooperate to produce an improvedand more sensitive X-ray measuring and testing system.

Other features and advantages not specifically enumerated will beapparent after a consideration of the following detailed description andthe appended claims.

In the drawings:

Fig. l shows diagrammatlcally an X-ray activated measuring deviceaccording to the invention; and

Fig. 2 illustrates graphically the operation of the invention in termsof voltage, X-ray beam intensity or signal intensity excited by theX-ray beam at various points in the device of Fig. 1.

When an X-ray tube is subjected to a cyclically variable power supplyfor the anode or target voltage, the output of the X-ray tube will varycorrespondingly in frequency and in intensity. lf this output impingeson a suitable X-ray responsive screen such as a fluorescent screen, thelight emitted by the screen will vary in consonance with the X-rayvariations, except for the inherent time lag of the fluorescentmaterial. If the light from the screen is projected on a photoelectriccell or the like, the time lag in the nuorescent screen will tend todisplace the instants of maximum and minimum excitation of the electrontube amplifier connected to the photoelectric cell, and thenon-linearity of response of the fluorescent screen to X-ray excitationsof different amplitude, will tend to reduce the difference between thesaid maximum and minimum amplifier excitation.

However, for a given X-ray tube operating with a certain voltage-timecharacteristic of the target or anode supply, during each of thesuccessive cycles of variation of that supply, all other factorsremaining the same, both the frequency spectrum and the intensity outputof the X-ray tube will vary in the same manner. That is to say, thefrequency of the X-ray spectrum and its intensity-versus-time will varywith the cyclical variation in the anode voltage supply. Therefore, theX-ray excitation of a fluorescent screen detector will follow anidentical pattern during the successive cycles and will transmitidentical excitations to an electron tube amplifier connected to thedetector and the peak, mean, or average values of these excitations,will remain identical over successive cycles.

These excitations being regularly recurrent and continuously variableover each cycle, are in accordance with the present invention, ampliedby an electron tube amplier of the alternating current type which can bedesigned so as to be sufficiently selective to respond only to a verynarrow frequency band corresponding to the frequency of excitation ofthe X-ray responsive fluorescent screen. This results in a correspondingdecrease in the noise level of the amplifier and an increasednon-responsiveness to extraneous undesirable excitations. Thesephenomena are graphically indicated in Fig. 2, with reference to theparticular apparatus of Fig. 1.

If, however, with an X-ray tube energized as above mentioned theintensity of the beam exciting the X-ray fluorescent screen is modulatedor changed to a new value by the introduction of an absorbing medium inthe X-ray path, the peak, mean or average value of the excitationvoltage impressed on the amplifier over each cycle will vary and thiswill correspondingly vary the output of the amplier. Therefore, thepeak, mean or average value of this amplied signal can be used, as ameasure of the absorption of the inserted medium, this measurement beingeither in absolute or relative values.

Such an arrangement is schematically illustrated in Fig. 1 of thedrawing, wherein there is represented any well-known form of X-ray tubeI. the anode or target 2 and the cathode 3 of which are supplied withpower from an A. C. supply source 4. The current through the X-ray tubeunder these circumstances will be a pulsating, intermittent directcurrent having a regularly recurrent component.

The X-ray beam from tube I is passed through a plurality of slits 1, 9,in alignment with which are two materials 9, III, one of which may be astandard of known density or X-ray absorption power, and the other ofwhich may be a material whose density or absorption power is to becompared with the standard. The divided beam, after passage through thebodies 9 and I9, impinges on two respective screens Il, I2, which havethe property of becoming fluorescent under X-ray excitation. Thesescreens may be of any construction well-known in the X-ray art. Thefluorescent light from each of the screens i I and I2 is projected uponthe photosensitive cathodes I3, Il, of a corresponding pair ofphotoelectric cells I5, I6, Whose anodes are respectively I1 and I8. Thecells I5 and I6 are connected to respective alternating currentamplifiers I9, 20. whose amplified outputs are applied respectively tosuitable meters or indicators 2|, 22. In accordance with the invention,the amplifiers I9 and are tuned so as to have a greater sensitivity atapproximately the frequency of the A. C. supply source 4. With thisarrangement, the amplifiers I9 and 2|! may be designed with therequisite stability and high gain so as to enable very much smallervariations between the divided portions of the X-ray beam to bedetected. For typical descriptions of a suitable organization of testingapparatus in which the system of Fig. l may be embodied, reference maybe had to the copending Fua and Woods application Serial No. 558,928,filed October 16, 1944. Since the sensitivity of the narrow bandalternating current amplifier I 9, 20, can be extremely high beforereaching the noise level, and as the gain of such an A. C. amplifier ismuch less responsive to voltage supply level variations and otherextraneous variations, than is a D. C. amplifier, the combination of anX-ray beam cyclically varied, and an A. C. amplifier as disclosed inFig. 1, will give an overall sensitivity not obtainable heretofore inthe detection and measurement of very Weak X-rays.

The various meters or indicators 2I, 22 can be calibrated under controlof a suitable calibrated gain control in the respective A. C.amplifiers, which gain controls can be designed and calibrated in termsof X-ray intensities or relative or absolute absorption powers ofarticles to be subjected to the X-ray excitation. Instead o! using twoseparate meters 2| and 22 as in Fig. 1, the outputs of the amplifiers I9and 2li can be fed in opposition to a single meter. No reading.therefore, will appear on this meter as long as the two screens I I andI2 are equally excited and if the gains of the amplifiers I9 and 20 arecorrectly balanced. If, however, an absorption medium IU of any kind isplaced in the path of one of the beams, a definite reading will show inthe output meter and this will be a measure of the X-ray intensitystriking screen I2 as compared to the steady excited screen I I. Such anarrangement has the advantage that the equipment is intensitive tofluctuations which affect the two portions of the divided beam equally.

It will be clear from the foregoing that, if desired, the alternatingpower supply 4 may be a specially designed A. C. power source having afrequency which is well removed from any disturbing frequencies. Forexample, if source 4 is of 25 cycles the equipment may be used quiteclose to powerful 60 cycle sources without introducing disturbances. Inthis event, of course, the ampliers I9 and 20 will be designed to have aband pass characteristic between 20 and 30 cycles and, if desired, Witha rejection lter for the 60 cycles.

I claim:

1. Apparatus for the testing of material by the precise and accuratemeasurement of X-ray penetrating the material including, in combination,an X-ray tube having conventional heated cathode and target anode, asource of alternating current of predetermined frequency and voltageimpressed across said cathode and anode, means for interposing materialto be tested in the path of an X-ray beam from said tube, a fluorescentscreen in the path of said beam beyond said material from said tube, anelectron-emissive photocell responsive to fluorescence of said screen,an alternating current amplier tuned to have a narrow band-passcorresponding to said frequency, said amplier receiving the output ofsaid photocell as input, and a quantitatively responsive meter formeasuring the amplitude oi the peaks of the output of said amplifier.

2. The method of detecting and precisely and accurately measuring smallvariations in the X- ray opacity of materials which includes feeding anX-ray source with an alternating current power supply, receiving a beamof X-ray from said source passed through the material to be tested upona fluorescent screen, permitting the fluorescence of said screen toactivate an electron-emissive photocell, feeding the output of saidphotocell to a highly selective alternating current amplifier, tuningsaid amplifier to have a narrow band-pass corresponding to the frequencyof said power supply, and precisely measuring the amplitude of the peaksof the output of said ampliler.

3. Apparatus for precisely and accurately measuring the X-ray opacityalong a, given path through an object to be measured which includes anX-ray tube having conventional heated cathode and target anode, a sourceof alternating current of predetermined frequency and voltage impressedacross said cathode and anode, means for passing a beam of X-ray fromsaid tube through the object to be measured, a fluorescent screenarranged to receive said beam after its passage through said object, anelectron-emissive photocell arranged to receive the uorescence from saidscreen, a comparison standard electric current having settable values ofan order comparable to those of the output current of said photocell,alternating current amplifying means responsive to said comparisoncurrent and said output current connected to said amplifying meansbetween said comparison current and said output current, and indicatormeans connected to said amplifying means for indicating the sign andmagnitude of the difference between said comparison current and saidoutput current.

4. Apparatus for precisely and accurately comparing physicalcharacteristics of a material with a standard sample of said materialwhich includes an X-ray tube having conventional heated cathode andtarget anode, a source of alternating current of predetermined frequencyand voltage impressed across said cathode and anode, means for denningtwo separate beams of X-ray from said tube, means for passing one ofsaid beams through the material to be compared, means for passing theother of said beams through the standard sample, a first iluorescentscreen arranged to receive the beam passing through the material to becompared, a second fluorescent screen arranged to receive the beampassing through the standard sample, a rst electron-emissive photocellarranged to receive the fluorescence of said first screen, a secondelectron-emissive photocell arranged to receive the fluorescence of saidsecond screen, alternating current amplifying means responsive to theoutputs of said photocells, and indicator means connected to saidamplifying means for indicating the difference between said outputcurrents.

5. Apparatus for precisely and accurately measuring the thickness of amoving web including, in combination, an X-ray tube having conventionalheated cathode and target anode, a source of alternating current ofpredetermined frequency and voltage impressed across said cathode andanode, means for defining two separate beams of X-ray from said tube,means for conducting the web across the path of one of said beams, meansfor interposing a standard sample of the web being measured in the pathof the other of said beams, a first fluorescent screen arranged toreceive the beam passing through the moving web, a second uorescentscreen arranged to receive the beam passing through the standard sample,a first electron-emissive photocell arranged to receive the fluorescenceof said first screen, a second electron-emissive photocell arranged toreceive the fluorescence of said second screen, alternating currentamplifier means responsive to the outputs of said photoeells, andindicator means responsive to the output of said amplifier means forindicating the diierence between said outputs.

References Cited in the iile of this patent UNITED STATES PATENTS NumberName Date 1,211,092 Coolidge Jan. 2, 1917 2,264,725 Shoupp et al Dec. 2,1941 2,301,251 Capen Nov. 10, 1942 2,513,818 Boop July 4, 1950 FOREIGNPATENTS Number Country Date 482,354 Great Britain June 19, 1936 30,371France Feb. 2, 1926 OTHER REFERENCES Fundamentals of EngineeringElectronics. Dow. published by John Wiley & Sons, Inc., New York city,1937; page 282. (Copy in Div. 54.)

Continuous Gaging With X-ray Micrometer, Woods and Fua, The Iron Age,November 29, 1945, pp. -51, Z50-83D.

